European Patent application no. 01650109, is directed to a method for rearing a bird of germ-free status comprising housing a parent bird, removing a premature egg in its shell from the parent bird prior to transfer of the premature egg to the cloaca and incubating the premature egg in its shell and hatching the premature egg to produce a laying bird.
Ventilation, temperature control and humidity are very important during the incubation and hatching process. The eggshell, in particular its pores and cuticle, modulate respiratory gas exchange and hydration of the developing embryo. Essentially, the eggshell is a breathable membrane and whilst the embryo is developing the eggshell allows carbon dioxide and water to escape from the egg and oxygen to enter the egg. As the embryo grows, it requires an increased supply of oxygen. Furthermore, care must be taken to maintain the appropriate humidity levels during the hatching period.
The conditions required for successful incubation and hatching of a normal, naturally laid egg are well known. These conditions vary between species. For example, for domestic fowl such as chickens, the entire process takes from 20 to 22 days, generally 21 days, with incubation conditions applying from Day 0 to Day 18 and hatching conditions applying from Day 18 to 21. During incubation eggs should be positioned so that the domed end, which contains the air cell, is uppermost. Typical incubator conditions are air temperature of 37.5° C., relative humidity (RH) of 50%, and regular turning (rocking) of the eggs so that the longitudinal axis of the eggs is slowly rotated through approximately 80° (40° each side of vertical) once every 45 to 180 minutes.
At 3 days prior to hatching, on or after Day 18, the embryos typically move into the hatching position within the egg. The eggs should no longer be turned at this stage. From Day 19 to 21 the relative humidity should be raised to approximately 60% to 70%. This high humidity level reduces moisture loss from the egg. It is also important to maintain adequate ventilation throughout the incubation and hatching stages to ensure that carbon dioxide and oxygen concentrations of normal air at standard atmospheric pressure (760 mmHg) are maintained.
Normally, during the incubation of an egg and prior to the hatching phase, by Day 18 or 19, the eggs loose approximately 13% of their initial weight. This weight loss is essential for the correct development of an egg.
European Patent no. 0 295 964 describes an in-vitro avian embryo culture technique. In particular, this specification is directed to the incubation of an embryo in a closed container after the embryo has been removed from its shell. The container used is preferably part of an egg shell which has been chosen from the same species as is being cultured or, in the terms of the present invention, from a similar hen. Similarly, European Patent no. 0 511 431 discloses an in-vitro culture method for a fertilised ovum of a hen in which an embryo which has just been fertilised is taken from an upper portion of the magnum of the oviduct of a hen within an hour or so after oviposition and then subsequently cultured. Both of these specifications merely disclose the artificial culturing of eggs which have been removed without their shell.
The present invention is directed to special techniques for the incubation and hatching of surgically-derived premature eggs in their shell, in particular those derived from the method of European Patent application no. 01650109. These techniques give improved results in terms of yield of surgically-derived eggs when compared to conventional egg incubation and hatching techniques.